Optional error code to flag missing return type when an argument has an annotation

[JukkaL]

It's pretty common to see functions like this:

def foo(x: str):
    ...
    return <something>

Note that the function foo has an implicit Any return type, which is likely not what the programmer intended.

Add a new error code (disabled by default since this is a backward compatibility break) that generates an error about a missing return type if at least one argument has an explicit type annotation. The error could be something like 'Function "foo" has no return type annotation', and perhaps add a note suggesting the use of -> None if the function never returns a value.

We might eventually enable the error code by default as part of a major mypy release, such as 2.0 or 3.0.

[hauntsaninja]

Look at the code paths for --disallow-incomplete-defs

[Aditya-Sakpal]

Is this issue already been resolved?

[AVUKU-PRAGATHESWARI]

Is this issue solved..?

[Cnoor0171]

@JukkaL Hi. Isn't this already the way mypy behaves when the flag --disallow-incomplete-defs is used? For example, if I run mypy --disallow-incomplete-defs example.py on this file

# example.py
def foo(x: str):
    return 123

I get

example.py:2: error: Function is missing a return type annotation  [no-untyped-def]
Found 1 error in 1 file (checked 1 source file)